1. Field of the Invention
The present invention relates to a high thermal conductive material having high thermal conductivity and a process for producing the same.
2. Description of Background Art
In recent years, electronic devices containing many semiconductor elements have rapidly become common. Due to the development of microfabrication technology, the degree of integration of semiconductor integrated circuits have further increased. Also, the speed and output of the circuits have increased. To efficiently actuate the electronic devices which incorporate the semiconductor elements, it is important to appropriately maintain the temperature of the elements. Therefore, efficient measures for cooling or radiating heat are indispensable.
A high thermal conductive material plays an important role in effectively discharging heat generated in the semiconductor elements and preventing a decrease in performance and reliability of the semiconductor elements.
As a constituent for the high thermal conductive material, a metal with good thermal conductivity such as copper or aluminum has been conventionally used.
At present, an IC chip such as a CPU or memory is designed to be driven with low power to achieve low power consumption. However, as the semiconductor elements are highly integrated and the area for forming the elements is enlarged, the size of the IC chip tends to increase.
To discharge heat efficiently, it is necessary to bond the high thermal conductive material to the elements with high accuracy.
As the size of the IC chip increases, stress generated by the difference in thermal expansion between a semiconductor substrate (a silicon substrate or GaAs substrate) and the high thermal conductive material increases. This may cause a decrease in accuracy in bonding the high thermal conductive material to the IC chip, detachment of the high thermal conductive material from the IC chip, or mechanical destruction of the high thermal conductive material.
Therefore, as the constituent for the high thermal conductive material, a material having a coefficient of thermal expansion almost the same as that of silicon (Si) or GaAs which is the semiconductor substrate and also having high thermal conductivity must be selected.
Various embodiments for improving the high thermal conductive material have been reported. For instance, it has been known to use Cu (copper)-W (tungsten), aluminum nitride (AlN), or Al (aluminum)-SiC as the high thermal conductive material.
In particular, Cu—W is a composite material utilizing the combination of high thermal conductivity of W and high thermal conductivity of Cu. Since this material can be mechanically processed with ease, Cu—W can be formed into a miniaturized product with a complicated shape and is suitable as the high thermal conductive material for a semiconductor device.
AlN is a material having high electrical insulation properties and a low dielectric constant. AlN can be subjected to various metallization processes and can exhibit well-balanced thermal conductivity and thermal expansibility. Since this material has a coefficient of thermal expansion almost the same as that of Si, AlN is suitable for a semiconductor device in which a silicon substrate is used as the semiconductor substrate.
Al—SiC has high thermal conductivity and can be formed by near net shape forming so that a lid shape or the like of IC components can be comparatively simplified. Therefore, Al—SiC is suitable as the high thermal conductive material for a semiconductor device.
However, with the development of an advanced information society, a high thermal conductive material having low thermal expansibility closer to that of a silicon chip, as compared with the above-described Cu—W and Al—SiC, and having thermal conductivity higher than that of AlN has been demanded, to deal with a further increase in performance of the semiconductor elements such as an increase in the output of laser diodes as transmission media in the advanced information society and an increase in the degree of integration, speed, and performance of LSIs.